Retinitis pigmentosa and retinoblastoma are important hereditary diseases that usually cause retinal dysfunction in the first decade or two of life. Thus, it is important to study genes and their protein products specific to the retina that may be abnormal either in function or concentration in these retinal diseases. As a model system for photoreceptor-specific proteins, we are studying the regulation of expression of interphotoreceptor retinoid-binding protein (IRBP), a retinoid-transport protein synthesized by the photoreceptor neuron and secreted into the interphotoreceptor matrix. In a second study, we have found that a specific cAMP-dependent protein kinase exhibits a defect in synthesis in human retinoblastoma tumor cells that is similar in osteosarcoma. Such a defect could cause the uncontrolled growth of retinoblastoma cells. In a third study, we have excellent new evidence for the general hypothesis of "transdifferentiation" because we have found that retinoblastoma cells highly express specific lens crystallins in vivo and in vitro.